Error correction encoding method, error correction decoding method, error correction encoding apparatus, and error correction decoding apparatus

ABSTRACT

An error-correction coding method and an error-correction decoding method, in which error detection and error correction for an audio signal can be carried out when a video signal and the audio signal are multiplexed and transmitted by a DVI, is provided.  
     After an error correction code is added to each of samples of the digital audio signal, continuous n (n: integer equal to or larger than 2) pieces of samples of the digital audio signal, to which error correction codes are added, are interleaved to generate a coded audio signal.

TECHNICAL FIELD

[0001] The present invention relates to an error-correction coding method and apparatus for performing error-correction coding in which error correction codes to be used for correcting transmission errors at a receiving end are added to a digital audio signal to be transmitted, when transmitting a digital video signal and the digital audio signal between a transmitting end and the receiving end through a digital interface means. Further, the invention relates to a error-correction decoding method and apparatus for performing, at the receiving end, error-correction decoding for the signal that has been coded by the error-correction coding method and apparatus and then transmitted.

BACKGROUND ART

[0002] Conventionally, for example, when transmitting a video signal to a liquid crystal monitor or a CRT, analog transmission using an analog RGB interface has been in the mainstream. However, the number of displayable pixels has previously been determined in the liquid crystal monitor, and digital transmission has received attention with proliferation of the liquid crystal monitor. Further, an increase in refresh rate is needed for a reduction in flicker, and high-speed data transmission is needed for image display on a wider screen. Since, in the conventional analog transmission, transmission distortion is considerable and ghosts are likely to occur, importance of digital transmission is increasing with improvement in image quality.

[0003] With the needs for digital transmission, in recent years, DVI (Digital Visual Interface) has received attention. The DVI is an interface for digital display connection which is defined by DDWG (Digital Display Working Group), and transfers data using plural data channels on the basis of TMDS (Transition Minimized Differential Signaling) technique. When adopting a digital transmission method using the DVI, high-quality video data with less transmission distortion can be provided by digital transmission at low cost.

[0004] As described above, by the adoption of the DVI, a higher-quality image can be obtained as compared with analog transmission. Further, in the DVI, there exists a blanking period when other data can be transmitted, besides a period for transmitting RGB (Red, Green, Blue) pixel data. It is possible to transmit, for example, an audio signal using this blanking period.

[0005] When transmitting a digital video signal, a transmission error such as bit corruption sometimes occurs. However, even when such transmission error occurs in transmitting a video signal, it is not very conspicuous on screen and, therefore, no serious problem occurs. However, when a transmission error occurs during transmission of such as an audio signal, noise or unusual sound might occur and, therefore, the error rate must be considered more strictly than in the case of transmitting a video signal. That is, when transmitting error-conspicuous data other than a video signal by using the blanking period of the DVI or the like, processing for error detection and error correction is required independently. However, in the standard of the interface for digital display connection which is defined by the DDWG (Digital Display Working Group), a construction for error detection and error correction for an audio signal has not been proposed.

[0006] The present invention is made to solve the above-described technical problems and has for its object to provide an error-correction coding method, an error-correction coding apparatus, an error-correction decoding method, and an error-correction decoding apparatus, which can perform error detection and error correction for an audio signal when transmitting multiplexed video signal and audio signal by a DVI.

DISCLOSURE OF THE INVENTION

[0007] According to the present invention (claim 1), there is provided an error-correction coding method for performing coding in which an error correction code to be used for correcting a transmission error at a receiving end is added to a digital audio signal to be transmitted, when transmitting a digital video signal and the digital audio signal between a transmitting end and the receiving end through a digital interface means, and the method includes: an error correction code addition step of adding an error correction code to each of samples of the digital audio signal; and an interleaving step of interleaving continuous n (n: integer equal to or larger than 2) pieces of samples of the digital audio signal to which error correction codes are added in the error correction code addition step, thereby to generate a coded audio signal.

[0008] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0009] According to the present invention (claim 2), in the error-correction coding method defined in claim 1, the digital interface means converts every continuous two bits of the coded audio signal generated in the interleaving step into a signal of continuous ten bits, and transmits the converted signals.

[0010] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0011] According to the present invention (claim 3), in the error-correction coding method defined in claim 2 wherein, in the interleaving step, continuous two samples of the digital audio signal, to which error correction codes are added, are interleaved to generate a coded audio signal.

[0012] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0013] According to the present invention (claim 4), in the error-correction coding method defined in claim 1, the digital interface means converts every continuous four bits of the coded audio signal generated in the interleaving step into a signal of continuous ten bits, and transmits the converted signals.

[0014] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0015] According to the present invention (claim 5), in the error-correction coding method defined in claim 4, in the interleaving step, continuous four samples of the digital audio signal, to which error correction codes are added, are interleaved to generate a coded audio signal.

[0016] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0017] According to the present invention (claim 6), there is provided an error-correction decoding method for performing, at a receiving end, error-correction decoding for a signal which has been coded and transmitted by the error-correction coding method defined in claim 1, when transmitting a digital video signal and a digital audio signal between a transmitting end and the receiving end through a digital interface means, and the method includes: a deinterleaving step of dividing a sequence of continuous bits of the coded audio signal generated by the error-correction coding method, sequentially bit by bit, into n (n: integer equal to or larger than 2) samples of the digital audio signal; and an error correction step of performing error detection and error correction for each of the samples of the digital audio signal which have been obtained in the deinterleaving step.

[0018] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0019] According to the present invention (claim 7), in the error-correction decoding method defined in claim 6, at the transmitting end, said digital interface means converts every continuous two bits of the digital audio signal which has been coded by the error-correction coding method defined in claim 1 into a signal of continuous ten bits and then transmits the signal; and at the receiving end, said digital interface means converts every ten bits of the coded digital audio signal which has been converted for every two bits into a signal of ten bits, into the original signal comprising continuous two bits.

[0020] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0021] According to the present invention (claim 8), in the error-correction decoding method defined in claim 7, in the deinterleaving step, a sequence of continuous bits of the coded audio signal which has been generated by the error-correction coding method defined in claim 1 is sequentially divided, bit by bit, into two samples of the digital audio signal.

[0022] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0023] According to the present invention (claim 9), in the error-correction decoding method defined in claim 8, in the error correction step, when performing error detection and error correction for each of the two samples of the digital audio signal which are generated in the deinterleaving step, if the error detection and error correction have succeeded for one of the two samples while an error is detected but the error position cannot be specified for the other sample, a bit in apposition of the other sample corresponding to the error position specified for the one sample is inverted and, thereafter, the other sample with the inverted bit is again subjected to error detection and error correction.

[0024] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0025] According to the present invention (claim 10), in the error-correction decoding method defined in claim 6, at the transmitting end, said digital interface means converts every continuous four bits of the digital audio signal which has been coded by the error-correction coding method defined in claim 1 into a signal of continuous ten bits and then transmits the signal; and at the receiving end, said digital interface means converts every ten bits of the coded digital audio signal which has been converted for every four bits into a signal of ten bits, into the original signal comprising continuous four bits.

[0026] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0027] According to the present invention (claim 11), in the error-correction decoding method defined in claim 10, in the deinterleaving step, a sequence of continuous bits of the coded audio signal which has been generated by the error-correction coding method defined in claim 1 is sequentially divided, bit by bit, into four samples of the digital audio signal.

[0028] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0029] According to the present invention (claim 12), in the error-correction decoding method defined in claim 11, in the error correction step, when performing error detection and error correction for each of the four samples of the digital audio signal which are generated in the deinterleaving step, if the error detection and error correction have succeeded for one of the four samples while an error is detected but the error position cannot be specified for another sample, a bit in a position of the other sample corresponding to the error position specified for the one sample is inverted and, thereafter, the other sample with the inverted bit is again subjected to error detection and error correction.

[0030] Therefore, it is possible to realize a system which effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0031] According to the present invention (claim 13), there is provided an error-correction coding apparatus for performing coding in which an error correction code to be used for correcting a transmission error at a receiving end is added to a digital audio signal to be transmitted, when transmitting a digital video signal and the digital audio signal between a transmitting end and the receiving end through a digital interface means, and the apparatus includes: an error correction code addition means for adding an error correction code to each of samples of the digital audio signal; and an interleaving means for interleaving continuous n (n: integer equal to or larger than 2) pieces of samples of the digital audio signal to which error correction codes are added by the error correction code addition means, thereby to generate a coded audio signal.

[0032] Therefore, it is possible to provide an error-correction coding apparatus which realizes a system that effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

[0033] According to the present invention (claim 14), there is provided an error-correction decoding apparatus for performing, at a receiving end, error-correction decoding for a signal which has been coded and transmitted by the error-correction coding apparatus defined in claim 1, when transmitting a digital video signal and a digital audio signal between a transmitting end and the receiving end through a digital interface means, and the apparatus includes: a deinterleaving means for dividing a sequence of continuous bits of the coded audio signal generated by the error-correction coding apparatus, sequentially bit by bit, into n (n: integer equal to or larger than 2) samples of the digital audio signal; and an error correction means for performing error detection and error correction for each of the samples of the digital audio signal which have been obtained by the deinterleaving means.

[0034] Therefore, it is possible to provide an error-correction decoding apparatus which realizes a system that effectively performs error detection and error correction for an audio signal, when a video signal and the audio signal are multiplexed and transmitted by a DVI.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a block diagram illustrating the construction of a digital signal transmission apparatus including an encoder which performs coding using an error-correction coding method according to an embodiment of the present invention.

[0036]FIG. 2 is a block diagram illustrating the construction of the encoder which performs coding using the error-correction coding method according to the embodiment of the present invention.

[0037]FIG. 3 is a diagram illustrating an example of construction of an error correction code addition means included in the encoder which performs coding using the error-correction coding method according to the embodiment of the present invention.

[0038]FIG. 4(a) is a diagram illustrating samples of an audio signal to be input to the error correction code addition means.

[0039]FIG. 4(b) is a diagram illustrating samples of a coded audio signal to which error correction codes are added.

[0040]FIG. 5 is a block diagram illustrating the construction of a digital signal reception apparatus including a decoder which performs decoding using an error-correction decoding method according to the embodiment of the present invention.

[0041]FIG. 6 is a block diagram illustrating the construction of the encoder which performs coding using the error-correction coding method according to the embodiment of the present invention.

[0042]FIG. 7 is a diagram for explaining the state where a bit error which has occurred in a transmission path when transmitting a digital signal using 2-10 conversion and 10-2 conversion, propagates into a signal after 10-2 conversion.

[0043]FIG. 8 is a block diagram illustrating the construction of a digital signal transmission apparatus according to a modification of the embodiment of the present invention.

[0044]FIG. 9 is a block diagram illustrating the construction of an encoder 803 included in a digital signal transmission apparatus 801 shown in FIG. 8.

[0045]FIG. 10 is a block diagram illustrating the construction of a digital signal reception apparatus according to the modification of the embodiment of the present invention.

[0046]FIG. 11 is a block diagram illustrating the construction of a decoder 1005 included in a digital signal reception apparatus 1001 shown in FIG. 10.

[0047]FIG. 12 is a diagram for explaining the state where a bit error which has occurred in a transmission path when transmitting a digital signal using 4-10 conversion and 10-4 conversion, propagates into a signal after 10-4 conversion.

BEST MODE TO EXECUTE THE INVENTION

[0048] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A description will be given of an example where the embodiment of the present invention is applied to a case where a digital video signal and a digital audio signal are transmitted between a transmitting end and a receiving end through a digital interface means that is in conformity with the standard of the interface for digital display connection which is defined by the DDWG (Digital Display Working Group). In the standard of the interface for digital display connection defined by the DDWG (Digital Display Working Group), for the purpose of preventing a signal traveling through a transmission path from becoming a DC-like signal in which DC components are biased, there is employed a transmission method in which, at the transmitting end, a digital video signal is subjected to 8-10 conversion for converting every 8 bits of the signal into a 10-bit signal while a digital audio signal is subjected to 2-10 conversion for converting every 2 bits of the signal into a 10-bit signal, and the converted signals are output to the transmission path; and at the receiving end, 10-8 conversion and 10-2 conversion are carried out to obtain the original digital video signal and digital audio signal, respectively.

[0049]FIG. 1 is a block diagram illustrating the construction of a digital signal transmission apparatus including an encoder that performs coding using an error-correction coding method according to the embodiment of the invention. In FIG. 1, reference numeral 101 denotes the digital signal transmission apparatus. Numeral 102 denotes an 8-10 conversion means for converting every 8 bits of an input video signal into a 10-bit signal. Numeral 103 denotes an encoder for converting an input audio signal into a coded audio signal to which an error correction code is added. Numeral 104 denotes a 2-10 conversion means for converting every 2 bits of the coded audio signal outputted from the encoder 103 into a 10-bit signal. Numeral 105 denotes a signal multiplexing transmission means for multiplexing the output of the 8-10 conversion means 102 and the output of the 2-10 conversion means, and transmitting the multiplexed signal.

[0050]FIG. 2 is a block diagram illustrating the construction of the encoder 103 included in the digital signal transmission apparatus 101 shown in FIG. 1. In FIG. 2, reference numeral 201 denotes an error correction code addition means for adding an error correction code to each of samples of the input audio signal, and numeral 202 denotes an interleaving means for alternately outputting the n-th sample and the (n+1)th sample, bit by bit, which samples have been given the error correction codes by the error correction code addition means 201.

[0051]FIG. 3 is a diagram illustrating an example of construction of the error correction code addition means 201 included in the encoder 103 shown in FIG. 2. In FIG. 3, reference numeral 301 denotes a delay means for delaying an input signal by one clock, numeral 302 denotes an exclusive OR means, and 303 denotes an AND means.

[0052] Next, the operation at transmission will be described. In FIG. 1, a digital video signal and a digital audio signal which are output from a signal source such as a DVD player are input to the digital signal transmission apparatus 101. Between the inputted digital video signal and digital audio signal, the digital video signal is converted for every 8 bits into a 10-bit signal by the 8-10 conversion means 102 (8-10 conversion). On the other hand, the digital audio signal inputted to the error correction coding apparatus 101 is input to the encoder 103.

[0053]FIG. 4(a) is a diagram illustrating samples of an audio signal to be input to the error correction code addition means 201 of the encoder 103. In FIG. 4(a), the upper stage shows a signal of sample 0 including data of L0 and R0, and the lower stage shows a signal of sample 1 including data of L1 and R1. Each sample is a 56-bit signal in which a 4-bit VUCP signal is added to each of 24-bit L channel data and 24-bit R channel data. The 56-bit audio signal shown in FIG. 4(a) is time-sequentially input to the error correction code addition means 201 in order of sample 0→sample 1→sample 2 (not shown)→ . . . In this embodiment, a cyclic code polynomial, G(x)=1+x6+x7+x8, is realized by the circuit structure including the 8 stages of delay means as shown in FIG. 3, and an 8-bit error correction code is generated and added to each sample. That is, in FIG. 3, the 56-bit audio signal is sequentially input as a data input under the state where a /T syndrome input is 1, and the /T syndrome input is made 0 at the timing when all of the 56 bits have been inputted, and an 8-bit signal outputted as a syndrome output when 8-bit shift operation is made under this state is added as an error correction code. Thereby, as shown in FIG. 4(b), the sample 0 is given an error correction code BCH0 while the sample 1 is given an error correction code BCH1, and these samples are sequentially output from the error correction code addition means 201. The interleaving means 202 temporarily holds the continuous two samples of the audio signal to which the error correction codes are added by the error correction code addition means 201, and takes out every one bit from these two samples alternately. Taking the samples shown in FIG. 4(b) as an example, the interleaving means 202 temporarily holds the audio signals with the error correction codes, which are supplied from the error correction code addition means 201 in order of sample 0, sample 1, and every one bit is taken out of the two samples alternately, in order of the 1st bit of sample 0, the 1st bit of sample 1, the 2nd bit of sample 0, the 2nd bit of sample 1, . . . , the 64th bit of sample 0, and the 64th bit of sample 1.

[0054] The coded audio signal interleaved by the interleaving means 202 (the audio signal to which the error correction code is added) is converted for every continuous two bits into a 10-bit signal by the 2-10 conversion means 104 (2-10 conversion).

[0055] The signal multiplexing transmission means 105 multiplexes the video signal that is 8-10 converted by the 8-10 conversion means and the coded audio signal that is 2-10 converted by the 2-10 conversion means 104, and transmits the multiplexed signal.

[0056]FIG. 5 is a block diagram illustrating the construction of a digital signal reception apparatus including a decoder for performing decoding using an error correction decoding method of the present invention. In FIG. 5, reference numeral 501 denotes the digital signal reception apparatus. Numeral 502 denotes a reception demultiplexing means for receiving the multiplexed signal transmitted from the digital signal transmission apparatus 101, and demultiplexing the signal into the 8-10 converted video signal and the 2-10 converted coded audio signal to output these signals. Numeral 503 denotes a 10-8 conversion means for converting every 10 bits of the 8-10 converted video signal into the original 8-bit signal. Numeral 504 denotes a 10-2 conversion means for converting every 10 bits of the 2-10 converted coded audio signal into the original 2-bit signal. Numeral 505 denotes a decoder for detecting and correcting a transmission error in the coded audio signal that has been 10-2 converted by the 10-2 conversion means 504.

[0057]FIG. 6 is a block diagram illustrating the construction of the decoder 505 included in the digital signal reception apparatus 501 shown in FIG. 5. In FIG. 6, reference numeral 601 denotes a deinterleaving means for dividing a sequence of continuous bits of the inputted coded audio signal, bit by bit, into two samples. Numeral 602 denotes an error correction means for detecting whether a transmission error exists or not by processing each sample of the coded audio signal obtained by deinterleaving by the deinterleaving means 601, and correcting a detected error.

[0058] Next, the operation at reception will be described. The reception demultiplexing means 502 receives the multiplexed signal transmitted from the digital signal transmission apparatus 101, demultiplexes the signal into the 8-10 converted video signal and the 2-10 converted coded audio signal, and outputs the 8-10 converted video signal and the 2-10 converted coded audio signal to the 10-8 conversion means 503 and the 10-2 conversion means 504, respectively. The 10-8 conversion means 503 converts every 10 bits of the inputted 8-10 converted video signal into the original 8-bit signal, and outputs the signal to a signal processing means (not shown) in the subsequent stage, such as a digital-to-analog converter. Further, the 10-2 conversion means 504 converts every 10 bits of the inputted 2-10 converted coded audio signal into the original 2-bit signal, and outputs the signal to the decoder 505. The deinterleaving means 601 in the decoder 505 divides (deinterleaves) the sequence of continuous bits of the coded audio signal outputted from the 10-2 conversion means 504, bit by bit, into two samples, and sequentially outputs these samples to the error correction means 602. The error correction means 602 is provided with a cyclic polynomial circuit having the same structure as that shown in FIG. 3, and the samples of the deinterleaved coded audio signal are successively inputted from a data input terminal of the cyclic polynomial circuit. When a 64-bit sample to which an error correction code is added is passed through the cyclic polynomial circuit, all of the last 8 bits of the syndrome output become 0 when there is no transmission error. The error correction means 602 judges that no transmission error occurs when all of the last 8 bits of the syndrome output are 0, and outputs a digital audio signal obtained by removing the error correction code from the inputted coded audio signal, to a subsequent signal processing means such as a digital analog converter (not shown). On the other hand, when all of the last 8 bits of the syndrome output are not 0, it is judged that there is a transmission error, and the error bit is specified by the following procedure, and then the specified error bit is inverted to correct the error and, thereafter, the digital audio signal from which the error correction code is removed is outputted to the subsequent signal processing means such as a digital analog converter. In the cyclic polynomial circuit shown in FIG. 3, when there is only one error bit in the inputted sample, 0 is continuously inputted from the data input, following the sample. If there is an error in the n-th bit of the sample, a bit string of a specific pattern appears in the syndrome output at the point in time when n bits of 0 are inputted, and thereby it is judged that an error occurs in the n-th bit of the sample.

[0059] In a digital signal transmission path having generally required performance, occurrence of plural bit errors in a short period is rare. However, like the standard of an interface for digital display connection that is defined by the DDWG (Digital Display Working Group), when employing a transmission method in which 2-10 conversion for a digital audio signal is performed at the transmitting end to output the signal to the transmission path, and 10-2 conversion is performed at the receiving end to obtain the original digital audio signal, since 10 bits are converted into a 2-bit signal in the 10-2 conversion, if there is one bit error in the 10-bit signal as shown in FIG. 7, the 10-bit signal does not indicate a correct 2-bit signal to be obtained any more, and it is considered that both of the 2 bits of the 2-bit signal after the 10-2 conversion might take wrong values. That is, one bit error that occurs during transmission might cause continuous two bit errors at the receiving end. Particularly in the standard of the interface for digital display connection that is defined by the DDWG (Digital Display Working Group), among the four kinds of 10-bit signals used for 2-10 conversion, there are 10-bit signals having a humming distance of 1, that is, 10-bit signals corresponding to different 2-bit signals, having only one bit as the number of portions having different bit patterns, and therefore, there is a high possibility that, when an error occurs, a 10-bit signal corresponding to a certain 2-bit signal might be changed to a 10-bit signal corresponding to another 2-bit signal. In this case, even when the signal including the continuous two bit errors is input to the cyclic polynomial circuit as shown in FIG. 3 to perform error detection, the error positions cannot be specified although it is judged that the signal includes the errors, and therefore, error correction cannot be carried out.

[0060] In the error-correction coding method and the error-correction decoding method according to the embodiment of the invention, at the transmitting end, interleaving is carried out after addition of error correction codes and then the interleaved signal is subjected to 2-10 conversion and transmitted, and at the receiving end, the 10-2 converted signal is deinterleaved and thereafter error detection and error correction are carried out. That is, the signal including continuous two bit errors as shown in the lowermost stage in FIG. 7 is subjected to error detection and error correction after being deinterleaved into two samples each including only one bit error. Thereby, the error positions can be specified by the cyclic polynomial circuit as shown in FIG. 3, and error correction can be carried out.

[0061] By the way, when employing the above-mentioned transmission method in which 2-10 conversion for a digital audio signal is carried out at the transmitting end to output the signal to the transmission path, and 10-2 conversion is carried out at the receiving end to obtain the original digital audio signal, if there is one bit error in the 10-bit signal, the 2-bit signal after the 10-2 conversion might become (0,0) although it has originally been (1,1), that is, both of the two bits might take wrong values. However, the 2-bit signal after the 10-2 conversion might become (0,1) or (1,0) which has originally been (1,1), that is, only one bit between the continuous two bits might take a wrong value. In the case where only one bit between the continuous two bits takes a wrong value, when the 10-2 converted signal is deinterleaved as in this embodiment, only one sample includes an error while the other sample includes no errors. It is now assumed that two transmission errors occur during transmission in a section to be two samples of the coded audio signal after the 10-2 conversion. When one of such two transmission errors is an error by which both of the two bits of the 2-bit signal after the 10-2 conversion take wrong values as in the case where the 2-bit signal which has originally been (1,1) becomes (0,0) while the other transmission error is an error by which only one bit between the continuous two bits takes a wrong value as in the case where the 2-bit signal which has originally been (1,1) becomes (0,1) or (1,0), when the 10-2 converted signal is deinterleaved, one sample includes two errors while the other sample include only one error. Accordingly, as for the sample including two errors, the error positions cannot be specified, and therefore, error correction cannot be carried out. However, as for the other sample including only one error, the error position can be specified, and thereby error correction can be carried out. Since it is estimated that the sample including two errors has an error in the same position as in the sample including one error, one of the errors included in the sample having two errors can be corrected using the result of error correction for the sample including one error. As a result, the sample which has included two errors becomes a sample including only one error, and this sample is again input to the cyclic polynomial circuit as shown in FIG. 3 to perform error detection, whereby the position of the remaining error can be specified, and all of the errors can be corrected.

[0062] Accordingly, in this embodiment of the invention, in the case where the error correction means 602 performs error detection and error correction for each of continuous two samples of the digital audio signal, when an error is detected in one sample but the error position cannot be specified while the other sample has succeeded in error detection and error correction, a bit in a position in the one sample corresponding to the error position specified in the other sample for which error detection and error correction have succeeded, is inverted and, thereafter, the sample with the inverted bit is again subjected to error detection and error correction, whereby the error correction rate can be increased.

[0063] As described above, according to the embodiment of the invention, when transmitting a digital video signal and a digital audio signal through a digital interface means between the transmitting end and the receiving end, at the transmitting end, after an error correction code is added to each of samples of the digital audio signal, continuous two samples of the digital audio signal to which the error correction codes are added are interleaved to generate a coded audio signal to be transmitted; and at the receiving end, the sequence of continuous bits of the received coded audio signal is divided (deinterleaved) bit by bit into two samples of digital audio signals and, thereafter, error detection and error correction are carried out for each sample of the digital audio signal obtained by the deinterleaving. Therefore, when a video signal and an audio signal are multiplexed and transmitted through a DVI, error detection and error correction for the audio signal can be effectively carried out.

[0064] In the above-described embodiment, 2-10 conversion for converting every two bits of a coded digital audio signal into a 10-bit signal is carried out at the transmitting end to output the signal to the transmitting path and then 10-2 conversion is carried out at the receiving end to obtain the original coded digital audio signal. However, multiple-bit conversion at signal transmission is not restricted to 2-10 conversion. When applying the present invention to a method employing n-m conversion as a multiple-bit conversion, continuous n pieces of samples of a digital audio signal to which error correction codes are added are interleaved to generate a coded audio signal, and a sequence of continuous bits of the coded audio signal is divided (deinterleaved) bit by bit into n pieces of samples of the digital audio signal, whereby the same effects as described for the embodiment can be achieved.

[0065] Hereinafter, a description will be given of a modification in which the present invention is applied to a system where 4-10 conversion for converting every four bits of a coded digital audio signal into a 10-bit signal at the transmitting end to output the signal to the transmission path, and 10-4 conversion is carried out at the receiving end to obtain the original coded digital audio signal at the receiving end.

[0066]FIG. 8 is a block diagram illustrating the construction of a digital signal transmission apparatus according to the modification. In FIG. 8, reference numeral 801 denotes a digital signal transmission apparatus. Reference numeral 802 denotes an 8-10 conversion means for converting every 8 bits of an inputted video signal into a 10-bit signal. Reference numeral 803 denotes an encoder for converting an inputted audio signal into a coded audio signal to which an error correction code is added. Reference numeral 804 denotes a 4-10 conversion means for converting every four bits of the coded audio signal outputted from the encoder 803 into a 10-bit signal. Reference numeral 805 denotes a signal multiplexing transmission means for multiplexing the output of the 8-10 conversion means 802 and the output of the 4-10 conversion means 804 to output the multiplexed signal.

[0067]FIG. 9 is a block diagram illustrating the construction of the encoder 803 included in the digital signal transmission apparatus 801 shown in FIG. 8. In FIG. 9, reference numeral 901 denotes an error correction code addition means for adding an error correction code to each of samples of an inputted audio signal, and numeral 902 denotes an interleaving means for cyclically outputting, bit by bit, the n-th sample, the (n+1)th sample, the (n+2)th sample, and the (n+3)th sample, which samples are given error correction codes by the error correction code addition means 901.

[0068] The error correction code addition means 901 included in the encoder 803 has the structure shown in FIG. 3 like the error correction code addition means 201 included in the encoder 103 shown in FIGS. 1 and 2.

[0069] Initially, the operation at transmission will be described. In FIG. 8, a digital video signal and a digital audio signal outputted from a signal source such as a DVD player or the like are input to the digital signal transmission apparatus 801. Between the inputted digital video signal and digital audio signal, every eight bits of the digital video signal are converted into a 10-bit signal by the 8-10 conversion means 802 (8-10 conversion). On the other hand, the digital audio signal inputted to the digital signal transmission apparatus 801 is inputted to the encoder 803.

[0070] In the error correction code addition means 901, a 56-bit audio signal as shown in FIG. 4(a) is time-sequentially inputted in order of sample 0→sample 1→sample 2 (not shown)→sample 3 (not shown)→ . . . In this embodiment, a cyclic code polynomial, G(x)=1+x6+x7+x8, is realized by the circuit structure including the 8 stages of delay means as shown in FIG. 3, and an 8-bit error correction code is generated and added to each sample. That is, in FIG. 3, the 56-bit audio signal is sequentially inputted from the data input under the state where the /T syndrome input is 1, and the /T syndrome input is made 0 at the timing when all of the 56 bits have been inputted, and an 8-bit signal which is outputted as a syndrome output when 8-bit shift operation is made under this state is added as an error correction code. Thereby, as shown in FIG. 4(b), an error correction code BCH0 is added to the sample 0 while an error correction code BCH1 is added to the sample 1, and these samples are sequentially output from the error correction code addition means 901. The interleaving means 902 temporarily holds the continuous four samples of the audio signal to which the error correction codes are added by the error correction code addition means 201, and cyclically takes out each bit from the four samples. Taking the sample shown in FIG. 4(b) as an example, the interleaving means 902 temporarily holds the samples of the audio signal to which error correction codes are added, which are supplied from the error correction code addition means 901 in order of sample 0, sample 1, sample 2, and sample 3, and cyclically takes out each bit from the four samples in order of the 1st bit of sample 0, the 1st bit of sample 1, the 1st bit of sample 2, the 1st bit of sample 3, the 2nd bit of sample 0, the 2nd bit of sample 1, the 2nd bit of sample 2, the 2nd bit of sample 3, . . . , the 64th bit of sample 0, the 64th bit of sample 1, the 64th bit of sample 2, the 64th bit of sample 3.

[0071] The coded audio signal which has been interleaved by the interleaving means 902 (the audio signal to which the error correction codes are added) is converted for every continuous 4 bits into a 10-bit signal by the 4-10 conversion means 804 (4-10 conversion).

[0072] The signal multiplexing transmission means 805 multiplexes the video signal that has been 8-10 converted by the 8-10 conversion means 802 and the coded audio signal that has been 4-10 converted by the 4-10 conversion means 804, and transmits the multiplexed signal.

[0073]FIG. 10 is a block diagram illustrating the construction of a digital signal reception apparatus according to the modification. In FIG. 10, reference numeral 1001 denotes a digital signal reception apparatus. Reference numeral 1002 denotes a reception separation means for receiving the multiplexed signal transmitted from the digital signal transmission apparatus, and separates the signal into the 8-10 converted video signal and the 4-10 converted coded audio signal to output these signals. Reference numeral 1003 denotes a 10-8 conversion means for converting every 10 bits of the inputted 8-10 converted video signal into the original 8-bit signal. Reference numeral 1004 denotes a 10-4 conversion means for converting every 10 bits of the inputted 4-10-converted coded audio signal into the original 4-bit signal. Reference numeral 1005 denotes a decoder for detecting and correcting a transmission error in the coded audio signal which has been 10-4 converted by the 10-4 conversion means 1004.

[0074]FIG. 11 is a block diagram illustrating the construction of the decoder 1005 included in the digital signal reception apparatus 1001 shown in FIG. 10. In FIG. 11, reference numeral 1101 denotes a deinterleaving means for dividing a sequence of continuous bits of the inputted coded audio signal, bit by bit, into four samples. Reference numeral 1102 denotes an error correction means for processing each sample of the coded audio signal obtained by deinterleaving by the deinterleaving means 1101, detecting whether there is a transmission error or not, and correcting a detected error.

[0075] Next, the operation at reception will be described. The reception separation means 1002 receives the multiplexed signal transmitted from the digital signal transmission apparatus 801, separates the signal into the 8-10 converted video signal and the 4-10 converted coded audio signal, and outputs the 8-10 converted video signal and the 4-10 converted coded audio signal to the 10-8 conversion means 1003 and the 10-4 conversion means 1004, respectively. The 10-8 conversion means 1003 converts every 10 bits of the inputted 8-10-converterd video signal into the original 8-bit signal, and outputs the signal to the subsequent signal processing means (not shown) such as a digital analog converter. Further, the 10-4 conversion means 1004 converts the every 10 bits of the inputted 4-10-converted coded audio signal into the original 4-bit signal, and outputs the signal to the decoder 1005. The deinterleaving means 1101 included in the decoder 1005 divides (deinterleaves) the sequence of continuous bits of the coded audio signal that is outputted from the 10-4 conversion means 1004, bit by bit, into four samples, and successively outputs the respective samples to the error correction means 1102. The error correction means 1102 is provided with a cyclic polynomial circuit having the same structure as that shown in FIG. 3, and the deinterleaved samples of the coded audio signal are successively inputted from the data input of the cyclic polynomial circuit. When a 64-bit sample to which an error correction code is added is passed through the cyclic polynomial circuit, all of the last 8 bits of the syndrome output become 0 when there is no transmission error. When all of the last 8 bits of the syndrome output are 0, the error detection means 1102 judges that there is no transmission error, and outputs the digital audio signal obtained by removing the error correction code from the inputted coded audio signal, to the subsequent signal processing means (not shown) such as a digital analog converter. On the other hand, when all of the last 8 bits of the syndrome output are not 0, the error detection means 1102 judges that there is a transmission error, and specifies an error bit in the following procedure, and inverts the specified error bit to perform error correction and, thereafter, outputs the digital audio signal from which the error correction code is removed to the subsequent signal processing means (not shown) such as a digital analog converter. In the cyclic polynomial circuit as shown in FIG. 3, when there is only one error bit in the inputted sample, 0 is continuously inputted from the data input, following the sample. When the n-th bit is an error bit in the sample, a bit string of a specific pattern appears in the syndrome output at the point in time when n bits of 0 have been inputted, and thereby it is judged that there is an error at the n-th bit in the sample.

[0076] In a digital signal transmission path having generally required performance, occurrence of plural bit errors in a short period is rare. However, like the standard of an interface for digital display connection that is defined by the DDWG (Digital Display Working Group), when employing a transmission method in which 4-10 conversion for a digital audio signal is performed at the transmitting end to output the signal to the transmission path, and 10-4 conversion is performed at the receiving end to obtain the original digital audio signal, since 10 bits are converted into one 4-bit signal in the 10-4 conversion, if there is one error bit in the 10-bit signal as shown in FIG. 12, the 10-bit signal does not indicate a correct 4-bit signal to be obtained by the 10-4 conversion any more, and it is considered that all of the 4 bits of the 4-bit signal after the 10-4 conversion might take wrong values. That is, only one bit error that occurs during transmission causes continuous four bit errors at the receiving end. In this case, even when the signal including the continuous four bit errors is inputted to the cyclic polynomial circuit as shown in FIG. 3 to perform error detection, the error positions cannot be specified although it is judged that the signal includes the errors, and therefore, error correction cannot be carried out.

[0077] In the error-correction coding method and the error-correction decoding method according to the modification, at the transmitting end, interleaving is carried out after addition of error correction codes and then the interleaved signal is subjected to 4-10 conversion and transmitted; and at the receiving end, the 10-4 converted signal is deinterleaved and thereafter error detection and error correction are carried out. That is, the signal including continuous four bit errors as shown in the lowermost stage in FIG. 12 is subjected to error detection and error correction after being deinterleaved into four samples each including only one bit error. Thereby, the error positions can be specified by the cyclic polynomial circuit as shown in FIG. 3, and error correction can be carried out.

[0078] By the way, when employing the above-mentioned transmission method in which 4-10 conversion for a digital audio signal is carried out at the transmitting end to output the signal to the transmission path, and 10-4 conversion is carried out at the receiving end to obtain the original digital audio signal, if there is one bit error in the 10-bit signal, the 4-bit signal after the 10-4 conversion might become (0,0,0,0) although it has originally been (1,1,1,1), that is, all of the four bits might take wrong values. However, the 4-bit signal after the 10-4 conversion might become (0,1,1,1) or (1,0,1,1) which has originally been (1,1,1,1), that is, only one bit among the continuous four bits might take a wrong value. In the case where only one bit among the continuous four bits takes a wrong value, when the 10-4 converted signal is deinterleaved as in this modification, only one sample includes an error while the other samples include no errors. It is now assumed that two transmission errors occur during transmission in a section to be four samples of the coded audio signal after the 10-4 conversion. In the case where one of such two transmission errors is an error by which all of the four bits of the 4-bit signal after the 10-4 conversion take wrong values as in the case where the 4-bit signal which has originally been (1,1,1,1) becomes (0,0,0,0) while the other transmission error is an error by which only one bit among the continuous four bits takes a wrong value as in the case where the 4-bit signal which has originally been (1,1,1,1) becomes (0,1,1,1) or (1,0,1,1), when the 10-4 converted signal is deinterleaved, one sample includes two errors while the other samples include only one error. Accordingly, as for the sample including two errors, the error positions cannot be specified, and therefore, error correction cannot be carried out. However, as for the other samples each including only one error, the error position can be specified, and thereby error correction can be carried out. Since it is estimated that the sample including two errors has an error in the same position as in the sample including one error, one of the errors included in the sample having two errors can be corrected using the result of error correction for the sample including one error. As a result, the sample which has included two errors becomes a sample including only one error, and this sample is again input to the cyclic polynomial circuit as shown in FIG. 3 to perform error detection, whereby the position of the remaining error can be specified, and all of the errors can be corrected.

[0079] Accordingly, in this modification, in the case where the error correction means 1102 performs error detection and error correction for each of continuous four samples of a digital audio signal, when an error is detected in one sample but the error position cannot be specified while the other samples have succeeded in error detection and error correction, a bit in a position of the one sample corresponding to the error position specified in the other samples for which error detection and error correction have succeeded, is inverted and, thereafter, the sample with the inverted bit is again subjected to error detection and error correction, whereby the error correcting rate can be increased.

[0080] As described above, according to the modification, when transmitting a digital video signal and a digital audio signal through a digital interface means between the transmitting end and the receiving end, at the transmitting end, after an error correction code is added to each of samples of the digital audio signal, continuous four samples of the digital audio signals to which the error correction codes are added are interleaved to generate a coded audio signal to be transmitted; and at the receiving end, the sequence of continuous bits of the received coded audio signal is divided (deinterleaved) bit by bit into four samples of the digital audio signal and, thereafter, each sample of the deinterleaved digital audio signal is subjected to error detection and error correction. Therefore, when a video signal and an audio signal are multiplexed and transmitted by a DVI, error detection and error correction for the audio signal can be effectively carried out.

APPLICABILITY IN INDUSTRY

[0081] The present invention provides an error-correction coding method, an error-correction coding apparatus, a error-correction decoding method, and an error-correction decoding apparatus, which realize efficient error detection and error correction for an audio signal when a video signal and the audio signal are multiplexed and transmitted by, for example, a DVI (Digital Visual Interface). 

1. An error-correction coding method for performing coding in which an error correction code to be used for correcting a transmission error at a receiving end is added to a digital audio signal to be transmitted, when transmitting a digital video signal and the digital audio signal between a transmitting end and the receiving end through a digital interface means, said method including: an error correction code addition step of adding an error correction code to each of samples of the igital audio signal; and an interleaving step of interleaving continuous n (n: integer equal to or larger than 2) pieces of samples of the digital audio signal to which error correction codes are added in the error correction code addition step, thereby to generate a coded audio signal.
 2. An error-correction coding method as defined in claim 1 wherein said digital interface means converts every continuous two bits of the coded audio signal generated in the interleaving step into a signal of continuous ten bits, and transmits the converted signals.
 3. An error-correction coding method as defined in claim 2 wherein, in said interleaving step, continuous two samples of the digital audio signal, to which error correction codes are added, are interleaved to generate a coded audio signal.
 4. An error-correction coding method as defined in claim 1 wherein said digital interface means converts every continuous four bits of the coded audio signal generated in the interleaving step into a signal of continuous ten bits, and transmits the converted signals.
 5. An error-correction coding method as defined in claim 4 wherein, in said interleaving step, continuous four samples of the digital audio signal, to which error correction codes are added, are interleaved to generate a coded audio signal.
 6. An error-correction decoding method for performing, at a receiving end, error-correction decoding for a signal which has been coded and transmitted by the error-correction coding method defined in claim 1, when transmitting a digital video signal and a digital audio signal between a transmitting end and the receiving end through a digital interface means, said method including: a deinterleaving step of dividing a sequence of continuous bits of the coded audio signal generated by the error-correction coding method, sequentially bit by bit, into n (n: integer equal to or larger than 2) samples of the digital audio signal; and an error correction step of performing error detection and error correction for each of the samples of the digital audio signal which have been obtained in the deinterleaving step.
 7. An error-correction decoding method as defined in claim 6, wherein at the transmitting end, said digital interface means converts every continuous two bits of the digital audio signal which has been coded by the error-correction coding method defined in claim 1 into a signal of continuous ten bits and then transmits the signal; and at the receiving end, said digital interface means converts every ten bits of the coded digital audio signal which has been converted for every two bits into a signal of ten bits, into the original signal comprising continuous two bits.
 8. An error-correction decoding method as defined in claim 7 wherein, in said deinterleaving step, a sequence of continuous bits of the coded audio signal which has been generated by the error-correction coding method defined in claim 1 is sequentially divided, bit by bit, into two samples of the digital audio signal.
 9. An error-correction decoding method as defined in claim 8 wherein, in said error correction step, when performing error detection and error correction for each of the two samples of the digital audio signal which are generated in the deinterleaving step, if the error detection and error correction have succeeded for one of the two samples while an error is detected but the error position cannot be specified for the other sample, a bit in a position of the other sample corresponding to the error position specified for the one sample is inverted and, thereafter, the other sample with the inverted bit is again subjected to error detection and error correction.
 10. An error-correction decoding method as defined in claim 6, wherein at the transmitting end, said digital interface means converts every continuous four bits of the digital audio signal which has been coded by the error-correction coding method defined in claim 1 into a signal of continuous ten bits and then transmits the signal; and at the receiving end, said digital interface means converts every ten bits of the coded digital audio signal which has been converted for every four bits into a signal of ten bits, into the original signal comprising continuous four bits.
 11. An error-correction decoding method as defined in claim 10 wherein, in said deinterleaving step, a sequence of continuous bits of the coded audio signal which has been generated by the error-correction coding method defined in claim 1 is sequentially divided, bit by bit, into four samples of the digital audio signal.
 12. An error-correction decoding method as defined in claim 11 wherein, in said error correction step, when performing error detection and error correction for each of the four samples of the digital audio signal which are generated in the deinterleaving step, if the error detection and error correction have succeeded for one of the four samples while an error is detected but the error position cannot be specified for another sample, a bit in a position of the other sample corresponding to the error position specified for the one sample is inverted and, thereafter, the other sample with the inverted bit is again subjected to error detection and error correction.
 13. An error-correction coding apparatus for performing coding in which an error correction code to be used for correcting a transmission error at a receiving end is added to a digital audio signal to be transmitted, when transmitting a digital video signal and the digital audio signal between a transmitting end and the receiving end through a digital interface means, said apparatus including: an error correction code addition means for adding an error correction code to each of samples of the digital audio signal; and an interleaving means for interleaving continuous n (n: integer equal to or larger than 2) pieces of samples of the digital audio signal to which error correction codes are added by the error correction code addition means, thereby to generate a coded audio signal.
 14. An error-correction decoding apparatus for performing, at a receiving end, error-correction decoding for a signal which has been coded and transmitted by the error-correction coding apparatus defined in claim 1, when transmitting a digital video signal and a digital audio signal between a transmitting end and the receiving end through a digital interface means, said apparatus including: a deinterleaving means for dividing a sequence of continuous bits of the coded audio signal generated by the error-correction coding apparatus, sequentially bit by bit, into n (n: integer equal to or larger than 2) samples of the digital audio signal; and an error correction means for performing error detection and error correction for each of the samples of the digital audio signal which have been obtained by the deinterleaving means. 